Glossary
HEAVY CHAIN DISEASES
Heavy chain diseases (HCDs) are rare lymphoplasmacytic B-cell proliferative disorders, characterized by the production of incomplete heavy chains or fragments thereof, with features resembling those of monoclonal immunoglobulin, lacking associated light chains. HCDs imply the presence of the three major classes of immunoglobulins that have been characterized as follows: the α-HCD form is the most common and presents the least amount of variations, whilst γ- and μ-HCD display considerable clinical and histopathological variability. HCDs can be thought of as a different types of non-Hodgkin lymphomas. α-HCD presents as lymphoma involving the extranodal marginal zone of the mucosa-associated lymphoid tissue; γ- HCD as non-Hodgkin lymphoplasmacytic lymphoma, and μ-HCD as small non-Hodgkin lymphocytic lymphoma or as chronic lymphocytic leukemia. HCDs diagnosis requires the detection of immunoglobulin heavy chain fragments in serum and urine in the absence of bound light chains. The prognosis may vary and there are no specific standardized treatment strategies with the exception of α-HCD, which may respond to antibiotic treatment in its early stages. Given the rarity of the disease, there have been cases in which the laboratory has helped clinicians in formulating a correct diagnosis. Immunofixation is a laboratory technique that employs specific antisera and reproducible methods in order to identify many proteins and their possible variants. The widespread use of monoclonal component characterization in serum and urine allows this method to be currently employed in most medium-large laboratories. Automation has contributed to make this electrophoretic technique simple and reproducible; nonetheless, the analyst’s protidological knowledge continues to play a key role in interpreting the various patterns and further steps to be taken in order to produce a report that may be compatible with the various associated pathologies. Heavy chain diseases are hard to identify among immunofixation patterns, thus requiring further tests in order to be validated. Methods aimed at highlighting the HCD are difficult to perform, requiring equipment that is often available only in university laboratories, or in those specialized in hematological disorders. Moreover, the presence of HCD always requires a multidisciplinary approach between the clinician and the clinical pathologist.
In fact, analysis of serum performed through electrophoretic techniques (capillary electrophoresis, gel electrophoresis) rarely yields monoclonal peaks, instead they often show up as increases in the gamma region or as slight increases in the beta1/beta2 zone.
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